The present invention relates to an image forming apparatus, such as printers, and more particularly to systems for monitoring and analyzing the calibration routines of the image forming device to predict print quality degradation.
Many image forming devices, e.g., copiers, printers, plotters, etc., include a controlling microprocessor which stores calibration data that enable adjustment of internal components in such a manner as to assure high quality document production. The calibration data is generally configured in the form of control parameters which are stored in either a random access memory or read-only memory, as the case may be. Control parameters can be stored directly on memory chips that are resident on replaceable consumable devices utilized with such devices.
In laser based printers, the electrophotographic process relies on control of toner particles and charge states. These fundamental materials and forces are influenced by a variety of external and internal conditions experienced in the printing process. For example, humidity, temperature, contaminants found on the surface of the photoreceptor, conditioning of the photoreceptor by previously printed patterns, manufacturing variations all affect the quality of printed image.
Electrophotographic printers include components that may be periodically tested and adjusted for changes in environment and/or operating conditions. For example, traditionally, toner cartridges have had life defined in terms of a toner load. The toner cartridge was considered good as long as there was toner available for printing. The advent of very large toner cartridges, e.g., with greater than 10,000 page capacity, has been accompanied by a new phenomena referred to as photoconductive (PC) drum wear out. With the use of a very large toner cartridge, the PC drum may wear out before the toner is expended. PC drum wear out occurs when low coverage or single page jobs are being printed and is caused by the number of rotations experienced by the PC drum. Newer technologies track the PC drum rotation and have established PC drum wear out limits that signal the end of the useful life of the toner cartridge.
Another new phenomena caused by the increased toner cartridge size is known as toner wear out. Toner wear out may occur when the toner in a toner cartridge is excessively stirred, which can be the result of low coverage, single page job printing or, in color printing, when one color is used very little but is rotated, e.g., in a carousel developer system. Toner wear out is different from PC drum wear out as it is not strictly a function of rotations, but is also a function of printed coverage. Toner wear out occurs when the materials designed to control flow and charge are displaced from the toner particle surface due to mechanical impact with container walls, handling components, or other toner particles. Removal of these materials cause the toner to charge or flow differently resulting in print quality defects.
Conventionally, image forming devices perform a calibration cycle to directly measure and adjust the control parameters for current changes in the environment and operating conditions, e.g., component wear out. A calibration cycle adjusts the control parameters of the image forming device only for present conditions and, thus, the calibration cycles will compensate for component wear out until failure actually occurs. Consequently, the calibration cycle will improve current image quality, but cannot predict when failure will occur, which may affect, e.g., a large print job.
Accordingly, what is needed is an apparatus and method of predicting when the print quality of the image forming device will degrade beyond acceptable limits, e.g., when system components will be worn out or exceed levels for which the device can compensate.
An image forming device, in accordance with the present invention, stores the correction factors produced during calibration cycles for future analysis. The correction factors, or alternatively, the new printer control parameters, which incorporate the correction factors, are normalized for current environmental conditions. During a calibration cycle, the normalized correction factors produced during the current calibration cycle and old normalized correction factors produced during prior calibration cycles are analyzed to determine if the printer control parameters are within desired degradation limits. Thus, a statistical analysis of the normalized historical data produced during calibration cycles can be used to predict when the image quality of the image printing device will degrade beyond acceptable limits. A system for enabling prediction of image degradation of an image forming apparatus, thus includes a means for calibrating the image forming device, which results in at least one correction factor, a memory for storing data, and a processor. In one embodiment, the system includes an environmental condition measuring device that is used to adjust the correction factors generated during the calibration cycle for environmental conditions. The processor analyzes the correction factors from the current calibration cycle, which may be adjusted for environmental conditions, as well as from previous calibration cycles to determine if the control parameters are operating within statistical acceptable control limits, which indicate, for example, that the print quality of the imaging forming device will degrade beyond acceptable limits prior to the next calibration cycle.
In accordance with another aspect of the present invention, a method for detecting print quality degradation in an image forming device includes performing multiple calibration cycles and analyzing the historical data obtained in the calibration cycles. The calibration cycles include generating at least one correction factor that is used to adjust at least one control parameter used to operate the image forming device. The present environmental conditions may be measured and used to adjust the correction factor produced in the present calibration cycle. The correction factor is stored so that it may be analyzed during future calibration cycles. The correction factor of the current calibration cycle and the correction factors of previous calibration cycles are analyzed to determine if the control parameters are within statistical acceptable control limits. If the analysis indicates that the control parameter is outside desired limits, a warning is provided to the user.